Occasionally it's useful to be able to determine a user's home directory
from within CLIPS. The CLIPS system command allows you to escape to the
operating system and execute a command to determine the home directory
(if the operating system provides such a command). However, since the
system command utilizes the C library routine system which has no return 
value, you can't directly return the value to CLIPS. You can get around
this problem by directing the output of the operating system command to
a file and then opening the file and reading the information from within
CLIPS. The following example shows how this can be done for the UNIX
operating system.

CLIPS>
(deffunction home-directory()
  (system "echo $HOME > home.txt")
  (open home.txt home)
  (bind ?home (readline home))
  (close home)
  (remove home.txt)
  ?home)
CLIPS> (home-directory)
"/neb_home/Riley"
CLIPS>
